Silicon controlled rectifier dimmer



July 6, 1965 S. J. SKIRPAN SILICON CONTROLLED RECTIFIER DIMMER Filed Feb. 25, 1960 3 Sheets-Sheet l a L f\ i INVENTOR.

July 6, 1965 Y 5. J. SKIRPAN 3,193,728

SILICON CONTROLLED RECTIFIER DIMMER Filed Feb. 25. 1960 3 Sheets-Sheet 2 IIO ,w 9 I Q: 70 n w 5 5O E 40 i z 10 so so 7o T j Y 'f POTIYFIOMTFQ S'TTING A N M es IN V EN TOR. STEPHEN K QMIY y 6, 1955 5. J. SKlRPAN 3,193,728

SILICON CONTROLLED RECTIFIER DIMMER Filed Feb. 25, 1960 3 Sheets-Sheet 3 A rropmsr United States Patent 3,193 728 SILICON CONTRGLLED RECTIFIER DIMMER Stephen J. Sirirpan, Flushing, N.Y., assignor to Ward Leonard Electric Co., Mount Vernon, N.Y., a corporation of New York Filed Feb. 25, 1960, Ser. No. 10,989 16 Claims. (Cl. 315-251) This invention relates to the adjusting of the level of intensity of incandescent lamps and the response of the adjusting apparatus to sudden heavy current drains or current surges.

This invention is particularly directed to the utilization of silicon controlled rectifiers for adjusting average lamp current and the protection of the silicon controlled rectifiers against excessive surge currents.

In prior systems the illumination was adjusted mechanically by varying a resistance or a transformer, or was adjusted electronically by a small voltage or current controlling a thyratron or magnetic amplifier. Both the thyratron and the magnetic amplifier have disadvantageous characteristics.

The silicon controlled rectifiers have a high gain and high current capacity. These rectifiers also rapidly respond to control currents and are light in weight and small in size. The disadvantage of the use of silicon controlled rectifiers as dimmers of incandescent lamps is the tendency to produce noise in the filaments of the lamps and the fragility to current surges in excess of the normal operating currents.

An object of the invention is to provide a silicon controlled rectifier dimmer that has a linear response to the dimmer controls and an automatic instantaneous protection against excess surge currents which is a common occurrence with tungsten lamp loads.

Another object of the invention is to provide protec tive means that resopnds promptly to the application of a low resistance load at full voltage to render the silicon controlled rectifiers non-conductive, and returns the silicon controlled rectifiers to a normal conductive condition within a brief period of time.

Another object of the invention is to provide a compact small dimmer that has a rapid linear response to the input control.

Other and further objects and advantages will be apparent from the following description taken in connection with the drawings, in which:

FIG. 1 is a diagrammatic illustration of the circuit;

FIG. 2 is a chart showing the relationship of the remote control setting and the R.M.S. output voltage;

FIG. 3 illustrates the wave form of the output voltage and the drive pulse;

FIGS. 4-A, B, C, D, E and FIGS. 5A., B, C, D, E, illustrate the response of the output voltage and current respectively in relation to time in cycles per second to the application of full incandescent lamp load with cold filaments to full output voltage; and

FIG. 6 is a diagrammatic illustration of a portion of the control circuit.

Dimmers using silicon controlled rectifiers consume relatively little power per kilowatt of control through intrinsic losses and are relatively light in weight per kilowatt and are of a relatively small size. Such dimmers have the further advantage of stable characteristics which remain stable throughout the life of the dimmer. These dimmers require protection against the application of incandescent lamps with cold filaments to the output of the dimmer when maximum drive signal is being applied to the rectifiers. The dimmer must limit lamp inrush current when such a load is applied to prevent destruction 3,193,728 Patented July 6, 1965 of the silicon controlled rectifiers. The time of output recovery however, should be less than one second.

In the embodiment of the invention alternating current is provided at the input terminals 10 and 11 to supply load current to the bank ofincandescent lamps 12 and the power stage 13 of the dimmer. The power stage controls the amount of average current flowing through the lamps and the power stage, and thus controls the intensity of illumination of the lamps. The illumination is adjusted from dim-out to full brilliance by the input control potentiometer 14 located on a remote control panel. The incandescent lamps 12 may be of the stage or television studio lighting type having a maximum total wattage of the order of 4 kilowatts. The conduction angle of and the amount of average current passed by the power stage is controlled by the pulse generator 15. The pulse generator produces a drive pulse or current. The phase angle of the drive pulse in relation to the anode voltage applied to the power stage is adjustable through by the control circuit 16.

The power stage 13 of the dimmer is of the bridge type with terminals 17, 18 connected in series with the incandescent lamp load 12 across the input terminals 16, 11. The main or load current passingthrough the lamps is controlled by the power stage. The power stage essentially comprises conventional silicon diodes 19, 2t) and 21 conducting current only in one direction and silicon controlled rectifiers 22, 23 of the pnpn type. This type of rectifier blocks current in one direction and con ducts current in the opposite direction on the application of a gating signal or drive pulse. Current is thereby blocked from passing to terminal 24 from terminals 17, 18 and current passes from the terminal 24 to terminals 17, 18 on the application of the drive pulse. The diodes 19, 20 are connected in one set of adjacent legs between the terminals 17, 18. The primary winding 26 of the inductor 27 is connected across the terminals 24, 25 diagonally opposite to the terminals 17, 18. The diode 21 is also connected across the terminals 24, 25 for reasons later described herein in connection with surge currents.

When the terminal 17 is positive with respect to terminal 18, current is blocked from passing through leg 28 by the silicon controlled rectifier 22. The diode 19 is in conductive relation to the polarity of the terminals and passes current through the leg. The diodes 20 and'21 are in a non-conductive relation to the polarity of terminal 17 and block the flow of current across the diagonal 29 and the leg 30. The only current path is through the inductor 26 from the terminal 25 to the terminal 24 on the opposite side of the diagonal. The conductivity of the silicon controlled rectifier 23 and leg 31 to the positive current of terminal 17 depends on the phase angle of the drive pulse applied to the gate electrode and the cathode of the rectifier 23. The load current then passes through the terminal 18 to the lamps 12. The phase relationship of the drive pulse to the input voltage determines the amount of current that will pass through the rectifier. Thus the silicon conrtolled rectifier 23 controls the amount of furrent and the illumination of the lamps on a half cyc e.

When the terminal 17 is negative and the terminal 18 is positive, current flows in-the reverse direction first passing through the lamps 12. The silicon controlled rectiher 23 blocks the current through the leg 31. The diode 20 is in conductive relation to the positive voltage of terminal 18 and conducts the current to the terminal 2-5. Diodes 19 and 21 are both in a non-conductive relation to the positive voltage of terminal 18. Therefore, the current passes through the inductor winding 26 in the same direction as when terminal 17 is positive. The silicon controlled rectifier 22 conducts the current depending on the degree of conductivity. The current then passes through the terminal 17 which is negative with respect to terminal 18. Thus the silicon controlled rectifier 22 determines the amount of current passed and the illumination in the other half cycle.

As seen from the foregoing description, a pulsating direct current is passed through the primary winding 26 of inductor 27. The resistance of winding 26 is very low so that only a small amount of power is lost in the winding. The main resistive load is the lamps 12. The winding 26 is magnetically coupled to the secondary winding 32. Under normal current conditions the pulsating direct current passing through the winding 26 saturates the inductor and little voltage is induced in the secondary winding 32. The secondary winding 32 is connected in a current loop comprising a diode 35, a zener diode 33 and a resistor 34. When a rapidly increasing current passes through the inductor winding 26, it produces a rapidly increasing voltage pulse in the secondary winding 32. This pulse, as later explained herein, is used to render the silicon controlled rectifiers non-conductive for a limited period of time.

The reverse characteristic of the silicon controlled rectifiers is similar to a silicon rectifier and presents an open circuit on application of a negative anode to cathode voltage. Current is blocked from flowing from the terminals 17 and 18 to the terminal 2 4. The forward characteristic is different and will conduct current above a critical positive anode to cathode voltage or below the critical voltage if an appropriate gate current signal is applied to the gate electrode. On application of the gate signal or drive pulse the silicon controlled rectifier will immediately become conductive and will have the characteristically low forward voltage drop of a single junction rectifier. The gate signal is applied to the silicon controlled rectifier on each half cycle and timed or fixed in relation to the half cycle to fire the silicon controlled rectifier over any portion of the half cycle. The earlier in the half cycle the rectifier is fired, the greater will be the amount of average current passed by the rectifier and greater will be the illumination of the lamps. Thus by varying the phase angle of the gate signal in the relationship to the alternating current, the illumination will be raised or lowered.

The gate signals or drive pulses are formed in pulse generator 15 and applied to the silicon controlled rectifiers by means of the transformer 36 having a primary winding 37 and two secondaries 38 and 39. The secondary windings are connected between the cathode and gate electrode of a respective rectifier. Diodes 4t 41 are connected between the secondaries and the gate to block the signal of opposite polarity from the signal producing conductivity.

The pulse generator may be of a conventional type. Alternating current is impressed across the reference terminals 42, 43. The terminals 42 and 43 are connected to the input terminals it), 11 and present a fixed reference voltage. The terminals 4 a, 44b are connected to the control circuit 16 which produces a direct current signal variable in voltage in relation to the setting of control potentiometer 14. The pulse generator comprises a phase shifting network 56 including the anode winding 48 of the reactor 4-7. The reactor 47 has two control windings 49 and 50. Control winding 59 is coupled to the secondary winding 32 of the inductor 27 to retard the pulse generator on an overload current in a manner later described herein. The control winding 49 is connected to the control circuit to impress a direct current signal for varying the phase of the output drive pulse in relation to the reference or input signal. This signal is impressed on the peaking transformer which produces a positive and negative pulse on each half cycle. These pulses are variable in phase in relation to the input voltage over a range of 180.

The output transformer has two separate secondary windings 33, 39 respectively connected to the silicon controlled rectifiers 22, 23. Winding 38 is connected across the cathode 52 and gate electrode 53 of the silicon controlled rectifier Z2, and winding 39 is connected across the cathode 54 and gate electrode 55 of the rectifier 23 to impress the drive pulse current on the respective rectifiers to render them conductive. The rectifiers 40 and 41 are connected in series with the windings 38 and 39, and in this embodiment of the invention between the windings and the gate electrodes to block the current of the opposite polarity. Since the rectifiers are connected in such a relation that the current or drive pulse of the other half cycle occurs when the rectifier is rendered non-conductive by the application of a reverse polarit only one of the pulses is effective in controlling the conductivity of the rectifier. Thus the conductivity of a rectifier occurs only on every other half cycle. The shifting of the phase of the pulse by the control circuit adjusts the point in the cycle when the pulse will render a respective rectifier conductive.

The control circuit 16 comprises an illumination control component 56 and a feedback component 57. The illumination control circuit has a low voltage signal transformer 58 with the primary winding 59 connected to the input terminals by the leads 61, 62. The secondary winding oil is connected across a control potentiometer 14 with the adjustable tap 63. The adjustable tap 63 and the terminal 64- at one end of the potentiometer are connected to opposite terminals of a diode bridge network formed by the diodes 65, 66, 67 and 68. The control winding 49 of the reactor 47, resistor 73 and resistor 74 are connected in series between the output terminals 6? and 70 of the diode bridge network. The variation in amplitude of the illumination control signal or command signal varies the inductance of reactor 47 and thereby the phase of the pulse produced by the pulse generator. This variation is, however, not linear unless a correction is applied. The feedback component or circuit 57 is connected across the load and develops a negative feedback voltage which when algebraically combined with the command signal produces a resultant signal that on variation in amplitude produces a linear R.M.S. output voltage across lamp load 12. The feedback component 57 may comprise a low voltage transformer 75 having a primary winding 76 connected across the lamps and a secondary winding 77. Diodes 78 and 79 are connect d respectively to opposite ends of the secondary winding to provide a unidirectional current through the output resistor 74. The series surge resistor 30 and the capacitor 81 provide a filtered DC. negative feedback reference voltage. The zener diode 82 and the capacitor 81 produce a combined action which closely approximates a true R.M.S. feedback voltage. This R.M.S. feedback voltage provides the correction so that the output of the control circuit has a R.M.S. linear relationship between the lamp illumination and the movement of the tap 63.

The zener diode 82 prevents the application of a nega tive feedback at low intensities. After the low range, the zener diode passes current and the feedback correction provides a substantial linear relation. The adjustable resistor 73 in series with the control winding and the feedback resistor 74 provides an adjustment of total and feedback command signal.

As previously stated, one of the shortcomings of silicon controlled rectifiers is the inability to carry high currents in excess of the maximum rated current for any length of time. This characteristic extremely limits the surge capacity. Tungsten filament lamps have a high current surge when rated voltage is applied to cold filaments. The surge has to be controlled so as not to exceed the capacity of the silicon controlled rectifiers. The current through the lamps passes through the inductor 26. The winding 32 is coupled to the winding 26 and therefore a high voltage pulse is introduced in winding 32 on the rapid increase in flux. Under this condition the zener diode 33 conducts and a high voltage pulse is impressed across the potentiometer 34 and the winding 5t) of the reactor in the pulse generator. The Winding 50 is in opposition to the winding 49.

In the instance of a high current surge, when full signal is applied to the dimmer, the current will continue to pass through one of the rectifiers until it is turned off by the reversal in polarity. In this initial stage the load current through the rectifiers and lamp is limited by the impedance of the inductor 26. The high voltage pulse produced in the winding 32 is of such a nature and the time constants of the pulse generator so designed that the drive pulse of the pulse generatoris retarded in phase for approximately 40 to 50 cycles. With the load current shut off by the effect of the high voltage pulse on the pulse generator there is no negative feedback applied to the component'57 and no voltage impressed on resistor 74. The signal voltage impressed across the zener diode 45 causes the diode to conduct current. This provides a slow recovery time constant for the pulse generator. The conductionangle of the drive pulses advances slowly and the incandescent lamp filaments heat slowly. In non-surge conditions the combined voltage of the bridge 71 and resistors 73, 74 is below the conducting voltage of the zener diode and the current passes through the control winding 49. In the first cycles the drive pulse is retarded to shut the rectifiers off. The pulse then gradually shifts in phase rendering the rectifiers conductive for longer periods of time. The short conductive periods slowly warm the filaments of the lamp so that full current may be passed through the rectifiers at the end of 40 to 60 cycles.

This is illustrated in FIGS. 4 and 5. FIG. 4-A illustrates the full output voltage being applied to the lamp load with little load current being drawn or a volume of low current which would render the rectifiers conductive. At a time slightly before time Zero, when one of the rectifiers is subjected to a high current surge by the placing of a lamp having a cold filament in the load, the inductor 27 limits the rise in current for the remaining portion of this half cycle. The current through the inductor produces the high voltage pulse previously described which renders the Zener diode 33 conductive and retards the drive pulse so that no current is passed by either rectifier for a period of approximately 10 cycles. As indicated in FIGS. 4-B and 5B the drive pulse has shifted in phase supply to permit a small amount of current to pass through the rectifiers. After cycles as illustrated in FIGS. 4C and 5-0, the pulse has further shifted to render the rectifiers conductive earlier in the half cycle and permit more current to pass therethrough. By the time 40 cycles have passed, the rectifiers are conducting nearly full load current and by 60 cycles the dimmer has completely recovered and is again operating under normal conditions.

A It is thus seen that the silicon controlled rectifiers are fully protected against a high surge current. The inductor limits the current during the first half cycle and creates the retarding pulse or signal. This signal acts on the pulse generator to delay the drive signal or pulse so that the silicon controlled rectifiers are rendered nonconductive for a period of approximately ten cycles and then gradually become conductive for longer portions of the half cycle as the phase relationship of the pulse graduallyshifts to full brilliance within approximately 60 cycles. During normal steady state current operation the inductor winding saturates and therefore presents a low impedance to the half cycles passing therethrough. However, on the application of a low resist time when the dimmer is set for full brilliance, the inductor limits the initial surge of current so that the rectitiers are not damaged.

" As seen from FIGS. 4-A and 5-A the protective response occurs in much less than a half cycle. This action is more rapid than the conventional protective switches 83.

The diode 21 connected across the diagonal of the bridge network is in series with the winding 26 and provides a current path for discharging the Winding 26 when both of the rectifiers are non-conductive.

In the foregoing description the silicon controlled rectifiers are referred to as rectifiers and the dry plate rectifiers, vacuum type rectifiers, diodes or the like, which pass current in one direction only, are referred to as diodes. The pulse generator 15, illumination control circuit and feedback circuit may be referred to as means for producing a drive pulse or signal variable in phase in relation to the voltage applied to the input terminals 10, 11. The power stage 13 may be referred to as cur rent control means and the silicon controlled rectifiers as current control elements.

From the foregoing description of the apparatus it is seen that an incandescent lamp dimmer is described which has a high wattage capacity and is relatively small in size and light in weight. The transformers 36, 47, 58 land are of a small size. The inductor 27 is the single heaviest unit. The rectifiers are small in size and low in weight but have large heat dissipation plates or fins which consume the greatest amount of space for a single component. The capacitors and resistors are of standard size. The potentiometer 14 is of a small size and may be mounted in a panel or console in an array of control potentiometers and other controls. The power stage, pulse generator, control unit and other components may be and usually are remotely located from the panel and from the incandescent lamps 12. The feedback circuit 57 provides for substantial correction to the signal applied to the pulsegenerator. Additional feedback circuits may 'beprovided to provide an almost linear relationship between the potentiometer 14 and the intensity of illumination of the lamps 12. All of the advantages of current control by silicon controlled rectifiers have been obtained with full protection from high inrush currents and a linear control over the range of dimout to full brilliance.

Various modifications and changes may be made in the various components as described without departing from the invention as set forth in the appended claims.

I claim:

' 1. Apparatus for controlling the load current supplied to an incandescen-t'la-mp load supplied from an alternating source comprising current control means having output terminals for connecting the current control means in series with an incandescent lamp load, said current control means having connected between said output terminals, a bridge network with silicon controlled rectifiers in adjacent legs for alternately passing load current and diodes in the other opposite adjacent legs, surge current limiting and wave shaping means connected across the diagonal opposite to said output terminal diagonal for passing the load current through each silicon controlled rectifier, means for forming drive signals in timed relation with. alternating volt-age appliedto said output terrninals and variable in phase relative to the applied voltage to control the conductivity of said silicon controlled rectifiers for passing the load current over a range from dimout to full brilliance, and means connecting said surge current limiting and wave shaping rneansand said drive signal forming means to impress a pulse on said drive signal forming means to alter the phase relation of drive signals and the applied voltage on application of a low resistance load to render said silicon controlled rectifiers initially non-conductive to block the passage of load current and gradually restore the phase relation of the drive signal and applied voltage in an initial period less than one second.

2. Apparatus as set forth in claim 1 wherein said surge current limiting and wave shaping means comprise an inductor windingand a second winding coupled thereto for creating a pulse induced by said inductor winding and said connecting means connects said secondary winding to said drive signal forming means and includes a zcner diode to pass the pulse when it exceeds a given value for retarding the drive signal for the initial period.

3. Apparatus as set forth in claim 2 wherein said means for forming a drive signal comprises a pulse generator connected to the output terminals and to the silicon rectifiers to impress a drive signal thereon, an illuminating control means connected to said pulse generator for applying a control signal variable in amplitude to adjust the phase relationship of the drive signal and the applied voltage over a half cycle to set the load current from full brilliance to dimout.

4. Apparatus as set forth in claim 3 wherein said illuminating control means comprises a control unit for producing a control signal variable in amplitude for adjusting illumination of the lamps over the full range of illumination and having a component modifying the control signal .to change the illumination linearly with respect to input control signal over an initial range from dimout and a feedback circuit connected across the load to provide a corrective voltage for control signals above the initial range to provide a substantially linear relationship between the illumination of the lamps and the input control signal from dimout to full brilliance.

5. Apparatus as set forth in claim 1 wherein said means for forming a drive signal comprises a pulse generator connected to the output terminals and to the silicon rectifiers to impress a signal thereon, an illuminating control means connected to said pulse generator for applying a control signal variable in amplitude to vary the phase relationship of the drive signal and the applied voltage, said illuminating control means including means connected to said surge current limiting and wave shaping means for suppressing the phase control signal to retard the advance of the phase of the drive signal on occurrence of load current surge.

6. Apparatus for controlling the illumination of an incandescent lamp load comprising an output power stage having silicon controlled rectifiers and an inductor winding having a low impedance to normal currents and opposing the rapid increase of excessive currents to restrict the maximum value capable of passage by a silicon controlled rectifier and connected in series with the incandescent lamp load, means for applying a drive pulse variable in phase relation to the voltage applied to said rectifiers to vary the period of conductivity of said silicon controlled rectifiers and thereby the amount of current passing through the lamp load, means coupling said inductor winding and said drive pulse means to impress a signal created by the rapid increase in flux from a surge current through said inductor winding to retard the drive pulse for maintaining said silicon controlled rectifier non conductive for a brief period.

7. Apparatus for controlling the load current supplied to incandescent lamps from an alternating input comprising an output power stage in series with the lamps across the alternating current input, said stage being in the form of a four legged bridge network with silicon controlled rectifiers in adjacent legs and an inductor winding connected across the output of the network and in series with said silicon controlled rectifiers for passing the load current, drive pulse creating means connected to said silincon controlled rectifiers to alternately control the conductivity of said silicon controlled rectifiers and thereby the amount of load current, means connected between said pulse creating means and said inductor winding to impress a drive pulse retarding signal on said drive pulse creating means on passage of surge current through said inductor winding to render said silicon controlled rectifiers nonconductive for a brief period of time.

8. Apparatus for controlling the illumination of an incandescent lamp load supplied with load current from an alternating source and comprising current control means connected in series with said lamp load and having current control elements destructible by currents slightly in excess of the normal rated current connected to alternately pass the load current and having a drive signal producing means connected to said current control elements to render the current control elements conductive by drive signals and varying the amount of current passed by said current control elements by varying the phase relation of the applied voltage and the drive signals and having means for initially limiting surge currents connected in series with said current control elements to pass the load current and producing a signal on occurrence of a surge, means for connecting said current limiting means with said drive signal producing means to vary the phase relation of the drive signal and the impressed voltage to render said current control elements non-conductive for an initial period on the application of a low resistance load and gradually increase the conductivity within a period of approximately one second.

9. Apparatus for controlling the load current supplied to a load subject to surge currents and comprising current control means connected in series with said load and having current control elements destructible by cur rents slightly in excess of the normal rated current connected to alternately pass the load current and having a drive signal producing means connected to said current control elements to render the current control elements conductive by drive signals and varying the amount of current passed by said current control elements by varying the phase relation of the applied voltage and the drive signals and having means for initially limiting surge currents connected in series with said current control elements to pass the load current and producing a signal on occurrence of a surge, means for connecting said current limiting means with said drive signal producing means to vary the phase relation of the drive signal and the impressed voltage to render said current control elements non-conductive for an initial period on the application of a low resistance load and gradually increase the conductivity within a short period of time.

10. Apparatus for controlling the load current supplied to a load subject to surge currents comprising an output power stage in series with the load across the alternating current input, said stage being in the form of a four legged bridge network with silicon controlled rectifiers in adjacent legs and an inductor winding connected across the output of the network and in series with said silicon controlled rectifiers for passing the load current, drive pulse creating means connected to said silicon controlled rectifiers to alternately control the conductivity of said silicon controlled rectifiers and thereby the amount of load current, means connected between said pulse creating mean and said inductor winding to impress a drive pulse retarding signal on said drive pulse creating means on passage of surge current through said inductor winding to render said silicon controlled rectifiers nonconductive for a brief period of time.

11. Apparatus for controlling the load current supplied to a load subject to surge currents in excess of the normal current comprising an output power stage having a silicon controlled rectifier for passing and controlling the amount of load current, means for applying a drive pulse variable in phase relation to the applied voltage to the said silicon controlled rectifier to vary the period of conductivity of said silicon controlled rectifier and thereby the amount of load current, an inductor connected in series with said rectifier to delay the increase in surge current while having a low impedance to normal currents, and means in series with said silicon controlled rectifier and coupled to said drive pulse means to detect the surge current and impress a signal created by the rapid increase in current to retard the drive pulse for maintaining said silicon controlled rectifier non-conductive for a brief period.

12. Apparatus for controlling the amount of load current comprising alternating load current carrying means receiving half cycles of the same polarity and including a solid state controlled device sensitive to destruction by peak currents exceeding permissible values for prescribed periods and passing a load current on being rendered conductive by a drive signal synchronized with the proper polarity of the applied voltage and remaining conductive until removal of the applied voltage of the proper polarity, phase control and drive signal forming means coupled to said solid state device to apply a voltage variable in phase to the applied alternate half cycle to render said solid state device conductive over at least a portion of the half cycle for varying the amount of load current passed by said solid state device, an inductive impedance means connected in series with said solid state device to limit the peak currents passing through said device to permissible values, and a phase retarder having a current sensing member coupled to the load current carrying means and connected to said phase control and drive signal forming means to delay the drive signal for restricting the load current below permissible values after the first half cycle in cooperation with the impedance means for discontinuing the passage of current in excess of rated values.

13. Apparatus for controlling the load current supplied to a load subject to surge currents in excess of the normalcurrent comprising an output power stage having a solid state controlled device for passing and controlling the amount of load current, means for applying a drive pulse variable in phase relation to the applied voltage to the said solid state controlled device to vary the period of conductivity of said solid state controlled device and thereby the amount of load current, an inductor connected in series with said solid state controlled device to delay the increase in surge current, and means in series with said solid state controlled device and coupled to said drive pulse means to detect the surge current and impress a signal created by the rapid increase in current for retarding the phase of the drive pulse to limit the amount of current passed to safe values.

14. Apparatus for controlling the current supplied to a load comprising a silicon controlled rectifier passing the load current, means for applying a signal to said rectifier variable in phase relation to the applied voltage for varying the amount of current passed by said silicon controlled rectifier to a load, inductive means connected in series with said silicon controlled rectifier to pass the load current at a low impedance and delay the rapid rise in current on conduction of said silicon controlled rectifier to eliminate radio frequency noise and to permit circuit breaker means to operate on overload currents.

15. Electrical control apparatus for controlling the current applied to an incandescent lamp load supplied from an alternating current source comprising silicon controlled rectifiers to pass alternating halves of an alternating load current, control means for providing pulses variable in phase in relation to the load current connected to said silicon controlled rectifiers for controlling the amount or" load current passing therethrough by varying the phase of the applied pulses, a control potentiometer having a linear movement connected to said control means for varying the phase of said pulses, a feedback circuit connected to the output of said silicon controlled rectifiers and connected to said control means to provide a corrective voltage to maintain a given relationship between the illumination of the lamps and the movement of the control potentiometer.

16. Electrical control apparatus for controlling the current applied to an incandescent lamp load supplied from an alternating current source comprising silicon controlled rectifiers to pass alternating halves of an alternating load current, control means for providing pulses variable in phase in relation to the load current connected to said silicon controlled rectifiers for controlling the amount of load current passing therethrough by varying the phase of the applied pulses, a control potentiometer connected to said control means to provide an imput control signal for varying the phase of said pulses, a feedback circuit connected to the output of said silicon controlled rectifiers and connected to said control means to provide a corrective negative feedback voltage to maintain a linear relationship between the root means square voltage applied to the lamp load and the input control signal and thereby increase control sensitivity at low and high control settings.

References Cited by the Examiner UNITED STATES PATENTS 2,395,626 2/46 Higgins 3 15-197 2,920,240 1/60 Macklem 315-312 2,925,546 2/60 Berman 32125 2,929,967 3/60 Birkenes 315--83 2,975,333 3/61 Bird 315-289 2,9985 47 4/61 Berman 315--200 3,142,781 7/64 Izenour 3 15-194 FOREIGN PATENTS 784,342 10/57 Great Britain.

OTHER REFERENCES Applications and Circuit Design Notes (A Survey of Some Circuit Application of Silicon Controlled Rectifier), SSPI bulletin D420-02, August 1959 (see page 12).

Electronic Design, Publication (Controlled Rectifier Power Supply is Short Circuit Portected), by B. Berman, page 168, Nov. 11, 1959.

HERMAN KARL SAALBACH, Primary Examiner.

ARTHUR GAUSS, GEORGE N. WESTBY, Examiners. 

1. APPARATUS FOR CONTROLLING THE LOAD CURRENT SUPPLIED TO AN INCANDESCENT LAMP LOAD SUPPLIED FROM AN ALTERNATING SOURCE COMPRISNG CURRENT CONTROL MEANS HAVING OUTPUT TERMINALS FOR CONNECTING THE CURRENT CONTROL MEANS IN SERIES WITH AN INCANDESCENT LAMP LOAD, SAID CURRENT CONTROL MEANS HAVING CONNECTED BETWEEN SAID OUTPUT TERMINALS, A BRIDGE NETWORK WITH SILCON CONTROLLED RECTIFIER IN ADJACENT LEGS FOR ALTRNATELY PASSING LOAD CURRENT AND DIODES IN THE OTHER OPPOSITE ADJACENT LEGS, SURGE CURRENT LIMITING AND WAVE SHAPING MEANS CONNECTED ACROSS THE DIAGONAL OPPOSITE TO SAID OUTPUT TERMINAL DIAGONAL FOR PASSING THE LOAD CURRENT THROUGH EACH SILICON CONTROLLED RECTIFIER, MEANS FOR FORMING DRIVE SIGNALS IN TIMED RELATION WITH ALTERNATING VOLTAGE APPLIED TO SAID OUTPUT TERMINALS AND VARIABLE IN PHASE RELATIVE TO THE APPLIED VOLTAGE TO CONTROL THE CONDUCTIVITY OF SAID SILICON CONTROLLED RECTIFIERS FOR PASSING THE LOAD CURRENT OVER A RANGE FROM DIMOUT TO FULL BRILLIANCE, AND MEANS CONNECTING SAID SURGE CURRENT LIMITING AND WAVE SHAPING MEANS AND SAID DRIVE SIGNAL FORMING MEANS TO IMPRESS A PLURS ON SAID DRIVE SIGNAL FORMING MEANS TO ALTER THE PHASE RELATION OF DRIVE SIGNALS AND THE APPLIED VOLTAGE ON APPLICATION OF A LOW RESISTANCE LOAD TO RENDER SAID SILICON CONTROLLED RECTIFIERS INITIALLY NON-CONDUCTIVE TO BLOCK THE PASSAGE OF LOAD CURRENT AND GRADUALLY RESTORE THE PHASE RELATION OF THE DRIVE SIGNAL AND APPLIED VOLTAGE IN AN INITIAL PERIOD LESS THAN ONE SECOND. 